There is a conventionally known method in which a relief image is transferred to be formed on a grained support to thereby prepare a printing plate. For example, Japanese Patent Publication Open to Public Inspection (hereinafter abbreviated to JP O.P.I.) No. 9501/1977 proposes a method in which a grained aluminum plate has thereon a light-sensitive layer and a cover sheet and, after being imagewise exposed, has the unexposed portions of the light-sensitive layer eliminated together with the cover sheet therefrom to thereby prepare a negative-type printing plate: and JP O.P.I. Nos. 184049/1991 and 172351/1992 propose a method in which a grained aluminum plate is laminated with an imagewise exposed light-sensitive layer and has the unexposed area alone of the layer transferred to thereby prepare a printing plate.
However, it was difficult to market the above printing plate-making method because nothing suitable as the grained support was available at all. The conventional mechanical graining emthod, which does not give uniform grain, makes it difficult to conduct uniform image transfer, so that the method is not suitable for the transfer-type image formation. The electrolytic etching method enables uniform graining, but the electrolytic etching in a hydrochloric acid bath or sulfuric acid bath forms crater-like grain, which prevents a resist material from extending over to the deepest part thereof at the time of the image transfer, resulting in a partial deterioration of the resist material's adhesion property and unsatisfactory printing durability. In a support anodized in the sulfuric acid bath, the adhesion of the transferred relief image to the grain was not sufficient, and no adequate printing durability was obtained.